Auto Parts: Air Compressor, airport limos, air conditioning compressor

Question
I bought a '95 E350 Shuttle Bus. It appears that the air compressor is not working. I have no idea where its located. Can someone give me some direction on this?

Answer
    I'm assuming that this is a big bus with a E350 cab in the front, and that what you are referring to is the compressor for the air brakes.  It is mounted on the front of the engine along with everything else, driven by a belt.  If we are talking about the air conditioning compressor, it is located in the same place.  If this is a very weird bus with a self-leveling air suspension (I've never seen one but I hear that some airport limos are built this way), it will probably have an electric pump mounted under the hood, although the custom nature of such a vehicle could result in the pump being mounted anywhere 'cause it's electric.